Coca-Cola
How much caffeine is in Diet Coke?
Data checked against the source on 2026-10-03 by Oleksii Y.
One 12 fl oz can of Diet Coke has 46 mg of caffeine, according to The Coca-Cola Company (coca-cola.com, US).
How Diet Coke compares
- Strength: 13 mg per 100 ml.
- One 12 fl oz can has as much caffeine as about half a cup of brewed coffee, which has 94.8 mg per 8 fl oz cup.
- Of the 22 other sodas in our soda chart, 2 have more caffeine per serving and 20 have less.
How much will be left at bedtime?
1 × 12 fl oz can of Diet Coke
Left at 11:00 PM (8 h later), average metabolism
≈ 15 mg
Range 7–23 mg (fast to slow metabolism)
46 mg is already at or under the 50 mg this tool aims to have left at bedtime.
What sleep studies found near this dose
- Gardiner et al. 2025 (randomized trial): In 23 healthy young men, 100 mg taken 12, 8 or 4 hours before bed had no significant effect on measured or self-rated sleep.
- Gardiner et al. 2023 (meta-analysis): To avoid losing sleep time, the authors suggest a coffee (107 mg per 250 ml) at least 8.8 hours before bed.
Estimate from a simple model: half-life of 3, 5 or 8 hours, 50 mg bedtime target. How we calculate
How long does Diet Coke stay in your system?
Our model halves caffeine every 5 hours for average metabolism, and every 3 or 8 hours for fast or slow metabolism. From one 12 fl oz can of Diet Coke (46 mg), about 23 mg is still in your body 5 hours later and about 12 mg after 10 hours. If you clear caffeine slowly (an 8-hour half-life), about 19 mg is left after 10 hours.
Estimated caffeine left at 11:00 PM from one 12 fl oz can (46 mg), using a half-life of 5 hours for average metabolism and 3 to 8 hours for the range. How we calculate
| Had at | Left at bedtime (average) | Range |
|---|---|---|
| 8:00 AM (15 h before bed) | ≈ 6 mg | 1–13 mg |
| 12:00 PM (11 h before bed) | ≈ 10 mg | 4–18 mg |
| 3:00 PM (8 h before bed) | ≈ 15 mg | 7–23 mg |
| 6:00 PM (5 h before bed) | ≈ 23 mg | 14–30 mg |
How many fit in a day?
Reference amounts are for caffeine from all sources combined. Counted at the upper end of the stated amount, one serving at a time:
- Up to 400 mg a day for most healthy adults (FDA, EFSA): about 8 servings.
- Up to 200 mg at one time for healthy adults (EFSA): about 4 servings in one go.
- Up to 200 mg a day in pregnancy (EFSA, NHS): about 4 servings.
These are reference amounts for groups of people, not a personal limit. Some people feel jittery or sleep worse on much less. See the cutoff calculator for timing.
Good to know
Coca-Cola's US FAQ gives 46 mg for Diet Coke against 34 mg for a 12 oz can of Coke.
Diet Coke vs other Coca-Cola drinks
- Coca-Cola Original Taste: Diet Coke has more caffeine than Coca-Cola Original Taste per 12 fl oz can: 46 mg vs 34 mg.
- Coca-Cola Zero Sugar: Diet Coke has more caffeine than Coca-Cola Zero Sugar per 12 fl oz can: 46 mg vs 34 mg.
- Caffeine-Free Coca-Cola: Diet Coke has more caffeine than Caffeine-Free Coca-Cola per 12 fl oz can: 46 mg vs 0 mg.
Common questions
How much caffeine is in Diet Coke?
The Coca-Cola Company (coca-cola.com, US) gives 46 mg of caffeine per 12 fl oz can.
How many Diet Coke servings can I have in a day?
The FDA and EFSA cite up to 400 mg of caffeine a day, from all sources combined, for most healthy adults. At 46 mg per 12 fl oz can, that is about 8 servings if Diet Coke is your only source. In pregnancy the reference is 200 mg a day.
How late can I drink Diet Coke?
One serving has about 46 mg, which is at or under the 50 mg our calculator aims to have left at bedtime, so it sets no cutoff for a single serving. Several servings add up.
Does Diet Coke have more caffeine than Coca-Cola Original Taste?
Diet Coke has more caffeine than Coca-Cola Original Taste per 12 fl oz can: 46 mg vs 34 mg.
How long does Diet Coke stay in your system?
Of the 46 mg in one 12 fl oz can, roughly 23 mg remains after 5 hours and 12 mg after 10 hours with our average 5-hour half-life. From fast to slow metabolism, 10 hours later it is between 5 and 19 mg.
Where the number comes from
- Diet Coke products. The Coca-Cola Company (coca-cola.com, US). Product text: "Caffeine Content: 46mg / 12 fl oz" Accessed 2026-10-02. Source ↗
- What is caffeine? The Coca-Cola Company (coca-cola.com, US). FAQ answer: "Coke's caffeine content is 34mg for a 12-oz can, and Diet Coke caffeine content is 46mg." Accessed 2026-10-02. Source ↗
Recipes and labels change. If a number here no longer matches the label, the label wins.
General information, not medical advice
If you feel unwell after caffeine — for example chest pain, a fast or irregular heartbeat that does not settle, fainting, confusion or trouble breathing — get urgent medical help. If you are pregnant or breastfeeding, under 18, take medication, or have a heart, liver or anxiety condition, high blood pressure or a sleep disorder, ask a doctor or pharmacist what amount is right for you.
Sources
- U.S. Food and Drug Administration (2024). Spilling the Beans: How Much Caffeine is Too Much? FDA Consumer Updates. fda.gov ↗
- European Food Safety Authority. Caffeine | EFSA. EFSA topic page (summary of the 2015 Scientific Opinion on the safety of caffeine). efsa.europa.eu ↗
- NHS. Foods to avoid in pregnancy. NHS. nhs.uk ↗
An app for better sleep is on the way
We’re working on a mobile app to help you sleep better. It isn’t out yet. Leave your email and we’ll let you know when it launches.